The present invention relates to a method for forming acid fluorides from olefins, carbon monoxide and anhydrous hydrogen fluoride. Specifically the present invention relates to a method of continuously forming an acid fluoride using anhydrous hydrogen fluoride an olefin and carbon monoxide wherein the polymerization and dimerization of the olefin is minimized and provision is made for the removal of heat created in the reaction.
Much of the art used in the production of acid fluorides actually relates to the production of carboxylic acids. Acid fluorides are typically produced by reacting carbon monoxide, an olefin and anhydrous hydrogen fluoride. This is disclosed in Koch U.S. Pat. No. 2,831,877. Typically the reaction is continued and water is added to the acid fluoride to form hydrofluoric acid and carboxylic acid. The present invention deals with the formation of the acid fluoride and is not necessarily directed to the formation of the carboxylic acid. However, the preferred embodiment of the present invention includes a hydrolysis step whereby the acid fluoride is reacted with water to form a carboxylic acid.
There are two major problems associated with the formation of acid fluorides. The first is the heat formed during the reaction. Since this is an exothermic reaction, there can be a great deal of difficulty with carrying away the reaction heat. This does not present a significant problem if the size of the reactor is so small that the reactor vessel can absorb the heat without being damaged and without the heat of the reactants exceeding the maximum permissable temperature. However, in larger reactors there is a significant problem with the formation of heat. This problem can typically be eliminated by use of a continuous reactor such as a plug-flow reactor in which the reactants are pumped through a tube which is surrounded with a water jacket or some other cooling process. The tube provides sufficient residence time to allow the reagents to react and provides a large amount of surface area to transfer the heat away from the reaction.
The second problem encountered during the formation of the acid fluorides is the dimerization of polymerization of the olefins used in the reaction. A typical means to avoid this problem in the past has been to constantly agitate the reagents to sufficiently disperse the olefin so that no localized area of high concentration of olefin occurs. A further means to prevent these side reactions is to maintain a sufficient concentration of CO in solution. This can also be accomplished by continuously mixing the reactants so that gaseous CO is constantly dispersed in the liquid HF and olefin mixture. Thus, as the CO which dissolved in the liquid is reacted, the dispersed CO readily dissolves and is available to react with the olefin. This is easily accomplished in a batch type reactor where a constant stirring can be economically achieved. Unfortunately, as stated above, the batch reactor presents the problem of cooling efficiency.
One possible method of overcoming these problems is to incorporate an in-line mixer with a tubular reactor wherein the hydrogen fluoride and carbon monoxide are mixed and forced into a tubular reactor. The olefin can then be admitted into the tubular reactor. The olefin can then be admitted into the tubular reactor at a plurality of injection points along the tubular reactor so that all of the olefin is not dispersed at once and the mixing requirements are minimized. In this manner, the turbulence created simply by the fluid flowing through the reactor is sufficient to maintain the olefin in the dispersed state, and more time is provided for the CO to disperse and dissolve in the liquid. However, this is costly and less efficient than the present invention.
Thus, according to the present invention, an olefin, CO and anhydrous hydrogen fluoride can be violently mixed together in one vessel referred to as an area of high turbulence and continuously injected into a tubular reactor where they form an acid fluoride. The tubular reactor does not require additional mixing vessels nor does the olefin need to be injected at various locations along the reactor.
This is particularly significant if the reactor is a tube bundle reactor with hundreds or even thousands of individual tubes. This invention discloses a method of overcoming these problems, yet allows the mass manufacture required to economically produce the acid fluorides and the carboxylic acids from the acid fluoride. The present reactor combines the stirring features of a batch reactor with the cooling abilities of a continuous flow tubular reactor.